Physics was originally part of philosophy, like Isaac Newton's observation of how gravity affects falling apples.

Physics used to be philosophy.

For centuries, natural philosophy covered physics, chemistry, and biology. Newton even titled his masterwork Philosophiæ Naturalis Principia Mathematica—"Mathematical Principles of Natural Philosophy."

Philosophy: When Science Was 'Natural Philosophy'

Aristotle was a major figure in ancient philosophy and developed a comprehensive system of thought including metaphysics, logic, ethics, politics, and natural science.[42]

Then the split.

As fields matured, they broke off from philosophy. The term gained a narrower meaning focused on metaphysics, epistemology, and ethics.

Philosophy: When Science Was 'Natural Philosophy'